Science Facing Aliens - Invasive Alien Species in Belgium - Belgian ...

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56 Our models predict a mean number of about 22 000 ring-necked parakeet breeding pairs (90 % confidence limits from 9 000 to 39 800 pairs) indicating that these parakeets could become one of the most numerous cavity-nesting birds in the region. BRT results confirm that parakeet abundance is highest in older forests in urban environments, while there is also evidence that they prefer smaller, more fragmented forests (Strubbe, Graham & Matthysen in prep.). The resulting abundance map (Figure2) indicates that parakeets are expected to reach their highest densities along the strongly urbanized south-north axis from Brussels to Antwerp, while eastwards, there also is ample habitat for the parakeet to spread into, with high predicted abundances around the cities of Leuven and south of Hasselt. Westwards, there is less suitable habit and moderately high abundances are only found around the cities of Ghent and Bruges. Our nuthatch model estimates the number of nuthatches to be 4 646 (2 929 - 6 776) breeding pairs, which agrees very well with the 4 740 to 5 750 pairs estimated in the Flemish and Brussels Breeding Bird Atlas (Vermeersch et al. 2006, Weiserbs & Jacob 2007). As expected from previous results, nuthatch numbers were negatively associated with parakeet abundance and we were able to extract a competition coefficient, quantifying the effect of parakeets on nuthatch densities. As our predictions of parakeet and nuthatch abundance and our estimate of the competition coefficient all have associated uncertainties (i.e. confidence intervals) , this leads to a number of possible scenarios. Figure 2. Region-wide predicted parakeet abundance. Number of breeding pairs per 5x5 km UTM grid were obtained by summing the predicted parakeet abundances for each forest fragment within each grid cell. Figure 3. Region-wide, long-term impact of parakeets on nuthatches according to a moderate scenario, i.e. taking the mean values for both parakeet and nuthatch abundance and competition strength. Number of breeding pairs lost per 5x5 km UTM grid were obtained by summing the predicted nuthatch losses for each forest fragment within each grid cell.
Thus, we calculated the region-wide, long-term parakeet impact using the mean estimates and the upper and lower confidence limits of our predictions and these calculations show that despite the high predicted parakeet abundances, total impact on nuthatches will probably only be small, and even in a worst case scenario, i.e. the maximum estimate for parakeet abundance and competition strength, only one third of the nuthatch population would be at risk. A more moderate scenario, i.e. taking the mean values for both parakeet and nuthatch abundance and competition strength, indicates a loss of 11 % of the nuthatches (i.e. 551 pairs, Strubbe, Graham & Matthysen, in prep.). In Figure 3, we visualized the predicted parakeet impact according to this moderate scenario. To conclude, we argue that the establishment of ring-necked parakeets should be prevented, but that in areas where they are currently present, there is no imminent ecological threat that calls for an eradication campaign. References Chiron F., Shirley S. & Kark S., 2009. Human-related processes drive the richness of exotic birds in Europe. Proceedings of the Royal Society B-Biological Sciences, 276: 47-53. DAISIE 2009. Handbook of Alien Species in Europe, Dordrecht: Springer Netherlands. Elith J., Leathwick J. R. & Hastie T. 2008. A working guide to boosted regression trees. Journal of Animal Ecology, 77: 802-813. Guisan A. & Zimmermann N. E., 2000. Predictive habitat distribution models in ecology. Ecological Modelling, 135: 147-186. Hirzel A., Hausser J., Chessel D. & Perrin N., 2002. Ecological Niche Factor Analysis : How to compute habitat suitability maps without absence data? Ecology, 83: 2027–2036. Lever C., 2005. Rose-ringed Parakeet (Ring-necked Parakeet) Psittacula krameri, p.: 124-130 Naturalized Birds of the World, London: T & AD Poyser. Liu H. & Stiling P., 2006. Testing the enemy release hypothesis: a review and meta-analysis. Biological Invasions, 8: 1535-1545. Martin K. & Eadie J. M., 1999. Nest webs: A community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management, 115: 243-257. Matthysen E., 1998. The Nuthatches, London: T & A. D. Poyser. Parker I. M., Simberloff D., Lonsdale W. M., Goodell K., Wonham M., Kareiva P. M., Williamson B., Von Holle B., Moyle P. B., Byers J. E. & Goldwasser L., 1999. Impact: Toward a Framework for Understanding the Ecological Effects of Invaders. Biological Invasions, 1: 3 - 19. Robb G. N., McDonald R. A., Chamberlain D. E., Reynolds S. J., Harrison T. J. E. & Bearhop S., 2008. Winter feeding of birds increases productivity in the subsequent breeding season. Biology Letters, 4: 220-223. Shwartz A., Strubbe D., Butler C., Matthysen E. & Kark S., 2009. The effect of enemyrelease and climate conditions on invasive birds: a regional test using the rose-ringed parakeet Psittacula krameri as a case study. Diversity and Distributions, 15: 310-318. Strubbe D. & Matthysen, E., 2007. Invasive ring-necked parakeets Psittacula krameri in Belgium: habitat selection and impact on native birds. Ecography, 30: 578-588. Strubbe D. & Matthysen E., 2009a. Establishment success of invasive ring-necked and monk parakeets in Europe. Journal of Biogeography: Accepted manuscript. Strubbe D. & Matthysen E., 2009b. Experimental evidence for nest-site competition between invasive ring-necked parakeets (Psittacula krameri) and native nuthatches (Sitta europaea). doi:10.1016/j.biocon.2009.02.026 Biological Conservation, In Press 57
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Welcome to the World? Non-native br
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these geese species exchange betwee
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